arc: Fix race condition in applying modal state.

components/exo/shell_surface.cc

Index: components/exo/shell_surface.cc
diff --git a/components/exo/shell_surface.cc b/components/exo/shell_surface.cc
index 00a36dafe34afe065a4edb1d2dce8b858e4dc83e..4ac81ab980bd8f07234ed5cea16ebc801cf14560 100644
--- a/components/exo/shell_surface.cc
+++ b/components/exo/shell_surface.cc
@@ -496,9 +496,28 @@ void ShellSurface::SetSystemModal(bool system_modal) {
         << "Only a window in SystemModalContainer can change the modality";
     return;
   }
+
+  if (system_modal == system_modal_)
+    return;
+
+  system_modal_ = system_modal;
+
+  if (!widget_) {

[reveman, 2017/03/11 00:45:08]

nit: I don't think we should have this warning. Seems like perfectly valid
behavior by a client to call this before the widget exists now. Please change it
to "if (widget_) UpdateSystemModal();".

[khmel, 2017/03/11 01:33:32]

Nice, done

+    DLOG(WARNING) << "Skip setting system modal state to " << system_modal_
+                  << " because window is not ready yet.";
+    return;
+  }
+
+  UpdateSystemModal();
+}
+
+void ShellSurface::UpdateSystemModal() {
+  DCHECK(widget_);
+  DCHECK(!system_modal_ ||
+         container_ == ash::kShellWindowId_SystemModalContainer);

[reveman, 2017/03/11 00:45:09]

nit: just DCHECK_EQ(container_, ash::kShellWindowId_SystemModalContainer) here
and add a if "container_ == ash::kShellWindowId_SystemModalContainer" check to
OnSurfaceCommit

[khmel, 2017/03/11 01:33:32]

Done.

   widget_->GetNativeWindow()->SetProperty(
       aura::client::kModalKey,
-      system_modal ? ui::MODAL_TYPE_SYSTEM : ui::MODAL_TYPE_NONE);
+      system_modal_ ? ui::MODAL_TYPE_SYSTEM : ui::MODAL_TYPE_NONE);
 }
 
 // static
@@ -766,6 +785,7 @@ void ShellSurface::OnSurfaceCommit() {
       DCHECK(!widget_->IsVisible());
       pending_show_widget_ = false;
       widget_->Show();
+      UpdateSystemModal();
     }
   }
 }